Methods for separating proteins from connective tissue

ABSTRACT

Methods and systems for separating muscle tissue from connective tissue are provided, in which animal tissue containing both muscle tissue and connective tissue is subjected to stress, and muscle proteins are separated from the connective tissue. Slurries of separated myofibrillar protein are also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 11/994,350 filed Dec. 31, 2007, entitled, “Systems and Methodsfor Separating Proteins from Connective Tissue,” which in turn is a U.S.national stage application under 35 U.S.C. 371 of InternationalApplication Serial No. PCT/US06/25020 filed Jun. 26, 2006 of the sametitle, which in turn claims the benefit of the filing date of U.S.Provisional Application No. 60/696,071, filed on Jul. 1, 2005, thecontents of which are incorporated herein by reference in theirentirety.

FIELD OF THE INVENTION

The invention relates to muscle protein processing.

BACKGROUND

Presently, there is an interest in expanding the use of muscle proteinsas food because of their functional and nutritional properties. Betteruse of these materials would be particularly important with low-valueraw materials for which there is currently little or no human food use,for example, fatty pelagic fish and deboned muscle tissue from fish,poultry, and meat processing. The use of these materials has beenhampered because of the loss of functionality of the proteins duringprocessing and/or difficulties in handling the proteins. For example,many current processes for separating protein from connective tissuefirst dissolve the muscle protein and then separate the muscle proteinfrom the connective tissue. However, the dissolved proteins may haveundesirable properties, such as a tendency to foam when exposed to airand agitated, e.g., as by centrifugation, and/or a tendency to react ordenature when in solution.

SUMMARY OF THE INVENTION

The invention is based, at least in part, on the discovery that muscleprotein can be separated from animal tissue on the basis of its lowerstrength than that of connective tissue. It has also been found that (1)muscle tissue hydrates more rapidly in the presence of water than doesconnective tissue; and (2) the tensile strength of muscle tissue fallswith hydration. Muscle tissue is separated from connective tissue on thebasis of these properties by hydrating animal tissue that includesmuscle and connective tissue to weaken the muscle tissue, and thensubjecting the animal tissue to low shear environment with tensilestress sufficiently strong to tear the muscle, both from the connectivetissue and from itself, but sufficiently weak to avoid tearing theconnective tissue. In this fashion, the muscle tissue is torn from theconnective tissue and reduced in particle size until it can be readilyseparated from the connective tissue, for example, by means of a screen.The weakening of the muscle tissue described herein can be hastened andenhanced by raising or lowering the pH of the slurry above that of thenatural muscle tissue.

In one aspect, the invention features methods of separating muscleprotein from connective tissue. A slurry is created by placing animaltissue, which includes at least muscle tissue and connective tissue, inan aqueous solvent. The slurry is then accelerated in a low shearenvironment, e.g., an environment that subjects the slurry to littleshear stress, but enables sufficient acceleration to provide a level oftensile stress that is below a level where a substantial fraction ofconnective tissue will tear and no less than a level where a substantialamount of tearing occurs in a muscle tissue. Muscle protein is thenseparated from the connective tissue.

Embodiments may include one or more of the following features.

The acceleration can be continuous acceleration in a low shearenvironment. Following the creation of the slurry, but prior to theacceleration, the slurry van remain relatively undisturbed for a periodof time, e.g., at least about 5 minutes, sufficient to allow the muscletissue to partially hydrate. Following the creation of the slurry, butprior to acceleration, fat content of the animal tissue can be reduced,e.g., by adjusting pH of the slurry to about an isoelectric point ofmuscle protein (e.g., to about 5.5), e.g., by reducing temperature ofthe slurry to about −1° C. and/or, e.g., by bubbling air into theslurry. The aqueous solvent can be water. The pH of the aqueous solventcan be between about 5.0 and 9.5.

Low shear acceleration can be created by pumping the slurry through apipe comprising a constriction. The slurry can be housed within a tankand the pipe can be configured to circulate the slurry out of the tank,through the constriction, e.g., a reduction in an inner diameter of thepipe, e.g., a narrowing, a baffle, or a valve (e.g., a ball valve), andback into the tank.

The steps of accelerating the slurry can be repeated several times,e.g., 2, 3, 4, 5, 6 or more times.

The protein can be separated by introducing the slurry into a refinerthat includes a screen configured to allow a substantial portion of theprotein to pass through the screen and to prevent a substantial amountof the connective tissue from passing through the screen. The screen canbe formed of a mesh having apertures, e.g., no larger than about 5 mm,e.g., between about 0.25 mm and about 3.0 mm, e.g., between about 0.5min and 1.5 mm or between about 0.25 mm and 0.5 mm. The refiner canhouse a paddle configured to rotate within a cylindrical screen at aspeed of e.g., no more than about 1000 RPM, e.g., no more than about 750RPM, 500 RPM, 250 RPM, 100 RPM, or 60 RPM.

The animal tissue can include fish, shellfish, squid, poultry, beef,lamb, or pork tissue.

Prior to creating the slurry, bones can be removed from animal tissuecontaining muscle tissue and connective tissue to form deboned animaltissue. The step of creating the slurry can include placing debonedanimal tissue into an aqueous solvent for at least 30 minutes.

The low shear, high acceleration environment can be controlled toprovide a level of tensile stress so that a substantial fraction of theconnective tissue will not tear, and a substantial fraction of themuscle tissue will tear. Shear can also be controlled to preventdenaturation of substantially all of the muscle protein.

In a another aspect, the invention features methods of processingprotein. Muscle protein is first separated from animal tissue, and theprotein is subsequently solubilized. At least 50% of the separatedmuscle protein remains undissolved during the separation step.

Embodiments may include one or more of the following features.

Substantially all of the muscle protein can remain undissolved duringthe separation step. The separated muscle protein can be solubilized byraising the pH of a slurry comprising an aqueous solvent and the proteinto a point at which at least 75% of the separated muscle proteindissolves, e.g., to a pH of at least about 10.5. The separated muscleprotein can be solubilized by lowering the pH of a slurry comprising anaqueous solvent and the muscle protein to a point at which at least 75%of the separated protein dissolves, e.g., to a pH of between about 2.5and about 3.5.

In still another aspect, the invention features a fluid compositioncontaining at least water and insoluble protein, wherein at least about50% of the insoluble protein is in myofibrillar filament form and thefluid includes substantially no connective tissue.

Embodiments may include one or more of the following features.

The protein can include myosin. At least about 75% of the myosin can bein myofibrillar filament form. The composition can include less thanabout 10% by weight of connective tissue, relative to the amount ofprotein in the slurry. The composition can include less than about 4% byweight of connective tissue, relative to the amount of protein in theslurry.

In another aspect, the invention features systems for separating muscleprotein from connective tissue. The systems include a first reservoir; afirst pipe in fluid communication with the reservoir and having aconstriction therein; a pump configured to pump fluid from the reservoirthrough the pipe; and a separation device in fluid communication withthe first reservoir.

Embodiments of the systems may include one or more of the followingfeatures.

The systems can also include a second reservoir, a second pipe in fluidcommunication with the second reservoir and the separation device andhaving a constriction therein, and a second pump configured to pumpfluid from the second reservoir through the second pipe. The first pipecan be connected at an outlet of the first reservoir and at an inlet ofthe first reservoir and configured to recycle fluid passed from theoutlet of the first reservoir through the first pipe and through theinlet back into the first reservoir. The pump should be a low shear pumpand can be a positive displacement pump, a centrifugal pump, a jet pump,a peristaltic pump, a rotary pump, a diaphragm pump, a vane pump, or areciprocating pump. The constriction can include a reduction in an innerdiameter of the pipe. The constriction can be a baffle or a valve, e.g.,a ball valve. The separation device can include a refiner. The refinercan include a screen having apertures, e.g., no larger than about 2 mm,e.g., no larger than about 0.25 mm. The refiner can include a paddleconfigured to rotate within a cylindrical screen. The paddle can bepitched to move material within the cylindrical screen from a first endto a second end.

In yet another aspect, the invention features methods of increasing theprotein content of meat. A slurry is created by placing animal tissueincluding muscle tissue in an aqueous solvent. The slurry is acceleratedin an environment that subjects the slurry to little shear stress, butenables sufficient acceleration to provide a level of tensile stressthat is no less than a level where a substantial amount of tearingoccurs in muscle tissue, to reduce the particle size of muscle tissue.The slurry is combined with meat.

Embodiments may include one or more of the following features.

The slurry can be combined with muscle tissue by injecting the slurryinto muscle tissue. At least about 50% of the insoluble protein in theslurry can be in myofibrillar filament form. The animal tissue can befurther ground prior to placing it in the aqueous solvent. The aqueoussolvent can contain substantially no salts.

Embodiments of the systems and methods herein may include one or more ofthe following advantages.

In the new methods, the proteins, mainly muscle proteins, are separatedfrom connective and other tissue prior to solubilization of theproteins, which eliminates the need for such separation once theproteins are solubilized. The separation of the muscle protein is moreefficient than current methods, having a greater yield of proteinsand/or a lower level of connective tissue or other undesirable tissue.The separated proteins are subject to less foaming, shear and/or heat,resulting in less denaturation than in conventional techniques. Asubstantial amount of the protein, for example, a substantial amount ofmyosin, is in its normal myofibrillar filament form, that is,undenatured. The new methods also enable differing muscle types to beseparated from each other, where the muscle types differ in tensilestrength and/or rate of hydration in the presence of water,

As used herein, “low shear environment” is an environment free fromperturbation by a shearing mechanism, e.g., a blade or a propeller. Alow shear environment can be within, for example, a container or vesselor a lumen of a cylinder, e.g., a pipe described herein. Low shearacceleration can be generated by accelerating a slurry described hereinusing a low shear pump, e.g., any piston pump. Skilled practitionerswill appreciate that the level of low shear and high tensile stressdepends on the raw materials used, for example, a low shear environmentfor beef tissue includes a different shear level than a low shearenvironment for fish tissue.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Although methods and materialssimilar or equivalent to those described herein can be used in thepractice or testing of the present invention, suitable methods andmaterials are described below. All publications, patent applications,patents, and other references mentioned herein are incorporated byreference in their entirety In case of conflict, the presentspecification, including definitions, will control. In addition, thematerials, methods, and examples are illustrative only and not intendedto be limiting.

Other features, objects, and advantages of the invention will beapparent from the following detailed description and drawings, and fromthe claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a flow chart of a method embodiment.

FIGS. 2A-2D are a series of schematic illustrations of a methodembodiment.

FIG. 3 is a schematic view of an embodiment of a system as describedherein.

FIG. 4A is a schematic diagram of an embodiment of a valve.

FIG. 4B is a schematic diagram of an embodiment of a baffle.

FIG. 5 is a perspective view, partially cut-away, of an embodiment of arefiner.

FIG. 6A is a top view of a portion of an embodiment of a system.

FIG. 6B is a perspective view of a cross-section of an embodiment of asystem.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

General Methodology

Animal tissue including muscle tissue is placed in an aqueous liquid,resulting in hydration of at least some of the muscle tissue. The animaltissue is subject to stress, e.g., tensile stress, for example, tensilestress in a low shear environment. The stress is selected to besufficiently strong to tear the muscle, both from any connective tissueand from itself, but sufficiently weak to avoid tearing connectivetissue. Muscle tissue is torn from the connective tissue and reduced inparticle size until the differential in particle size between the muscletissue and connective tissue is large enough to permit separation ofmuscle tissue from connective tissue by a separation device, forexample, a screen. The application of stress in a low shear environmentand the separation of muscle from connective tissue can be carried outin a variety of ways and by a variety of systems as discussed in greaterdetail below. The key is to selectively break down the muscle tissueinto small particles, while leaving as much of the connective tissueintact as possible. Thereafter, they can be separated by size.

Typically, without intending to limit the invention and for descriptivepurposes only, the methods described herein can be analogized toattempting to separate spaghetti noodles from rubber bands. A mixture ofspaghetti noodles and rubber bands is placed in water, wherein thespaghetti hydrates. When this mixture is accelerated in a low shearenvironment to produce tensile stress, the spaghetti breaks into smallerand smaller pieces, while the rubber bands might appear generally thesame. After a few cycles of such acceleration, the spaghetti is in verysmall pieces, e.g., so small that they are not visible to the naked eye,and the mixture appears as a syrupy substance (containing tiny spaghettipieces) with relatively undisturbed rubber bands. This mixture is thenpassed through a screen with holes large enough for spaghetti particlesto pass through, but small enough to exclude the rubber bands. Theseparated spaghetti particles can be subsequently solubilized.

One embodiment of method 300 is illustrated in FIG. 1, where theseparation of muscle tissue from connective tissue begins by combininganimal tissue 310 and an aqueous liquid 311, e.g., water, in a reservoirtank 314 to create a slurry 312. The animal tissue may include proteins(e.g., muscle proteins), connective tissue, and other undesirabletissues, for example, small bones, cartilage, or blood. Any aqueoussolvent, e.g., buffered water, can be employed as the aqueous liquid.The aqueous liquid and animal tissue are in certain embodiments mixed ina ratio of at least 0.1 part water to 1 part animal tissue (e.g., atleast 1 part water to 1 part animal tissue, at least 1.5 parts water to1 part animal tissue, at least 2 parts water to 1 part animal tissue, atleast 5 parts water to 1 part animal tissue, at least 10 parts water to1 part animal tissue, at least 25 parts water to 1 part animal tissue,at least 50 parts water to 1 part animal tissue, or at least 100 partswater to 1 part animal tissue). Generally, a higher amount of waterresults in a faster hydration of the tissue, while a lower amount ofwater requires less dewatering and generates less waste. Ratios ofbetween 1 and 5 parts water to 1 part animal tissue generally provideacceptable hydration speeds and waste levels.

The pH of the aqueous solvent is generally selected to avoid foamingthat might occur if a substantial amount of protein were to dissolve,and is typically between about 4.2 and about 9.5 (e.g., between about5.0 and 8.5, e.g., between about 5.0 and about 7.5, between about 5.5and about 7.0). In certain embodiments, the slurry naturally fallswithin an acceptable pH range, and no further pH control is required.The slurry contains undissolved protein, e.g., muscle protein, andinsoluble material, e.g., connective tissue, and may, in someembodiments, additionally contain solubilized material, e.g.,solubilized proteins.

The slurry 312 in step 315 may, in certain embodiments, be allowed toremain relatively undisturbed for a period of time sufficient to permitat least some hydration of the muscle tissue (e.g., at least about 1, 2,5, 10, 20, 30, 40, 50, 60, 70, 80, or 90 minutes). In other embodiments,the slurry is processed immediately, i.e., the slurry is not allowed toremain undisturbed for any extended period of time. The slurry 312 may,in certain embodiments, be stirred to promote water uptake by the muscletissue. The temperature of the water is selected to prevent thedegradation of the protein filaments while permitting water uptake bythe muscle fibers, and can be, for example, no less than about 0° C.(e.g., no less than about 10° C., 20° C., 30° C., 40° C., 50° C., 60°C., 70° C., 80° C., 90° C., 100° C., 120° C., or 140° C.). As the muscletissue hydrates, the tensile strength of the muscle tissue decreases,resulting in an increase in the differential between the tensilestrength of the muscle tissue and the tensile strength of the connectivetissue.

In step 316, the slurry 312 is subjected to a tensile stress withminimal shear, e.g., by rapidly accelerating the slurry (such as, forexample, by pumping the slurry through a pipe having a constriction, bystirring the slurry, e.g., with a mixer such as, for example, an orbitalmixer, or by agitating the slurry, e.g., mechanically orultrasonically). The tensile stresses are controlled so as to be below alevel where a substantial fraction (e.g., over 80%) of connective tissuewill fail (e.g., tear), but at or above a level where a substantialfraction (e.g., over 80%) of the muscle tissue will fail (e.g., tear). Alow shear, high tensile stress environment can be generated, e.g., byaccelerating the slurry through a pipe, e.g., with smooth walls, with alow shear pump, e.g., a piston pump. A skilled practitioner willappreciate that a level of shear and tensile stress can be adjusteddepending on the type of raw materials used.

A visual test can be used to determine whether the amount of tensilestress applied is sufficient. Initially, the slurry observed by nakedeye in the reservoir tank contains tissue with large visible pieces ofmuscle and small pieces of connective tissue, e.g., tendons. Once thetissue is subjected to sufficient tensile stress, for a sufficientlength of time, the appearance of the slurry changes to a watery orsyrupy solution (containing reduced muscle protein) with small pieces ofconnective tissue. Thus, observing the slurry after subjecting it totensile stress, but before separating the muscle protein from theconnective tissue, can be used to determine whether the applied tensilestress is sufficient.

In addition, the amount of tensile stress applied can be measured with afiber optical stretch meter and/or by monitoring energy or work appliedto a certain amount of raw material. For example, the amount of energyconsumed or work done can be measured by monitoring additional amperagedrawn by a pump when either a valve is closed or a constriction imposed.The level of tensile stress sufficient to process tissue depends on thetype of muscle present, e.g., the amount of tensile stress (as measuredby applied energy or work) is about four times higher for processingbeef muscle than for processing fish muscle. The level of tensile stressalso depends on the length of time the stress is applied, e.g., thelonger the time, the lower the stress level that is required. A skilledpractitioner will be able to adjust tensile stress and/or applied energyas needed for a given application.

Where a pipe with a constriction is employed, the flow speeds requiredto achieve the desired forces will depend on the internal diameters ofthe pipe and the configuration of the constriction. Generally, forexample, where a reduction fitting is employed, the velocity v₂ of thefluid in the reduced diameter section can be determined by the equation:v ₂=(r ₁ ² /r ₂ ²)v ₁where: r₁=the internal radius of the pipe,

r₂=the internal diameter of the smaller end of the reduction fitting,and

v₁=the velocity of the fluid in the larger pipe

v₂=the velocity of the fluid in the smaller pipe.

For example, in a system running at 20 gallons per minute (“GPM”), theinitial velocity would be 0.9 ft/sec through a 3-inch ID pipe. When thefluid passes through a constriction made up of a 3-inch long reducerdown to a 1-inch ID pipe, in a linear distance of two inches, thevelocity of the fluid increases to 8 ft/sec, in that the fluid spends,on average 0.09 seconds in the reducer described at a flow of 20 GPM,the average acceleration in the direction of flow is 80 ft/sec².Acceleration can be controlled by altering the extent and/or length ofthe constriction and/or the flow rate. It should be noted that theacceleration shown in the above calculation is a fraction of the averagetotal acceleration caused by the restriction, as acceleration exists indirections other than the positive direction of flow. The magnitude ofthe forces that the solid particles are subjected to can be altered bychanging the size and shape of the restriction or by increasing ordecreasing the rate of flow. For example, the system described abovecould be made to run, e.g., at least 5 ft/sec² acceleration, by runningit at a flow rate of 5 GPM. Alternatively, a high acceleration of, e.g.,504 ft/sec² could be achieved at 50 GPM.

The upper limit of acceleration will, in certain embodiments, be thelevel at which the temperature of the slurry is raised above a desiredlimit, e.g., a temperature above which denaturation of the muscleprotein occurs. In certain embodiments, using a sufficient number ofcycles removes the need for a lower limit on acceleration, e.g.,acceleration can be lower than 5 ft/sec². Extremely gentle accelerationmay be needed to separate weak forms of connective tissue, e.g.,membranes. A higher level of acceleration may be needed to separatecoarse tissue, e.g., beef. Skilled practitioners will appreciate thatthe acceleration level needs to be adjusted according to the type oftissue used and the total time the tensile stress is to be applied. Inone embodiment, all acceleration can occur in the area of the reductionfitting.

In certain embodiments, a refrigeration apparatus may be placeddownstream of the area of acceleration to remove any generated heat andpotentially limit denaturation and/or other heat-related problems. Ofcourse, the stress associated with acceleration is not the only stressapplied by the system. Turbulence contributes to the stress applied,both the turbulence of passing through the conduit and the increase inturbulence resulting from the constriction, along with any elbows orother changes in pipe direction. In general, the amount of energy putinto the system can be measured or approximated by changes in theamperage drawn by the pump motor or by directly measuring the pressuredrop across the constriction, along with the flow rate. Work deliveredto the slurry per unit time can be kept constant or can be varied overthe course of a batch operation. Generally, the rate of acceleration orwork can be controlled by monitoring the amperage and/or flow rateand/or the pressure drop, and adjusting the pump speed and/or thecross-sectional area of the constriction. The system described herein isflexible, in that its operation can be controlled by adjusting flowrate, restriction size, and/or time the slurry spends in variouscompartments.

Upon being subjected to high tensile and low shear force, for example,resulting from the acceleration of the aqueous solvent and slurry, theweaker muscle tissue will begin to break into smaller pieces, while theconnective tissue will tend to remain substantially intact. Further, themuscle tissue will break away from the connective tissue, effecting aseparation of the two components. Such is illustrated in FIGS. 2A-2D inthe context of pumping the slurry through a restriction fitting in apipe. An animal tissue fragment 200 made up of a piece of connectivetissue 202 and a piece of muscle tissue 204 is being pumped through apipe 208 having a reduction fitting 210 located in the pipe 208. As theanimal tissue fragment 200 approaches the reduction fitting 210 in FIG.2A, the fluid flow rate begins to increase. The increase in flow rateaffects the downstream end 205 of the animal tissue fragment 200 priorto its affecting the upstream end 206 of the animal tissue fragment 200,pulling the downstream end 205 along and stretching the animal tissuefragment 200 in the direction of fluid flow.

When the change in flow rate is of sufficient force, this stretchingresults in a tear 212 in the muscle tissue, seen in FIG. 2B, andeventually to the separation of the muscle fragment 204 into two smallermuscle tissue fragments 204 a and 204 b, as illustrated in FIG. 2C. Theacceleration forces also result in a tear 214 between the muscle tissuefragment 204 b and the connective tissue fragment 202, which eventuallybecomes complete, resulting in muscle tissue fragment 204 b pullingloose from connective tissue fragment 202, illustrated in FIG. 2D. Thus,the initial animal tissue fragment 200, which included both muscletissue and connective tissue, is broken into two smaller fragments ofmuscle tissue (204 a and 204 b) and a separate fragment of connectivetissue 202. Each smaller fragment has a higher surface-to-volume ratiothan the larger fragment 200, which can facilitate further hydration (byexposing new surfaces to water).

Referring again to FIG. 1, the shiny 312 can then be directed into areservoir tank in step 318. The reservoir tank may be the same reservoirtank 314 from which it was pumped or may be a different reservoir tank.The slurry can then be allowed to hydrate further, and subjected tofurther high tensile and low shear force by being accelerated through apipe having a constriction (step 316) for a second time. The hydrationand acceleration steps (e.g., steps 315, 316 and 318) can be repeated asoften as necessary to achieve the desired results. For example, thehydration and acceleration steps can be run once, or no less than twice(e.g., no less than three times, no less than four times, no less thanfive times, no less than six times, no less than seven times, no lessthan eight times, no less than nine times, no less than ten times, noless than fifteen times, no less than twenty times). Additional animaltissue and/or aqueous solvent may be added at any of the steps, e.g.,water can be added to replace water taken up by the muscle tissue,particularly where the water to animal tissue ratio is initially small,e.g., 0.5 parts water to 1 part animal tissue. Additionally, thehydration times and temperature and the amount of acceleration forcescan be held constant throughout, or can be adjusted from cycle to cycle.For example, the hydration times for subsequent hydration steps can bemade shorter, as the surface area of the muscle tissue increases.

As the muscle tissue breaks into smaller fragments, the surface area tovolume ratio increases, as discussed above. This increase in surfacearea enables further hydration of the muscle tissue (by exposing newsurfaces), further weakening the muscle tissue and enabling the muscletissue to break down into smaller and smaller fragments or particles.

The slurry 312 can then be pumped from the reservoir 314 to a separationdevice, here a refiner 320, where the insoluble material, e.g.,connective tissue 322, is separated from the slurry; leaving anseparated isolated) protein slurry 324, which can be further processedas desired. When so desired, the muscle tissue particles can be reducedin size (in steps 315, 316 and 318) until the muscle tissue takes on apaste-like consistency. The refiner can include a screen, e.g., acylindrical screen, with holes of, for example, from about 0.25 mm toabout 2 mm. The mesh size is selected to exclude substantially all ofthe connective tissue, as the paste-like slurry of muscle tissueparticles will readily pass through a small mesh. Skilled practitionerswill appreciate which mesh size is appropriate for a given application.

Fragments of the connective tissue, which have a higher tensile strengththan the muscle tissue and which hydrate and lose tensile strength at alower rate than the muscle tissue, remain sufficiently large that theywill not readily pass through the small mesh screen in the refiner butinstead will be pushed out of the refiner terminal end by the paddles,thus separating the protein, mainly muscle protein, from the connectivetissue. In some embodiments, the hydration time, the acceleration force,and the number of cycles can be adjusted to reduce the muscle tissue toan extremely small size, whereby the refiner can be replaced with arotary or a tangential screen that separates the protein, mainly muscleprotein, from the connective tissue without the use of paddles.

In-Line Continuous Systems

An embodiment of a system for separating muscle protein from connectivetissue is illustrated in FIG. 3. The system 10 includes a series ofreservoir tanks 12, 14, and 16. Pipes 20 and 22 lead from the reservoirtank 12 to the reservoir tank 14 and from the reservoir tank 14 to thereservoir tank 16, respectively. The pipes 20 and 22 have pumps 30 and32, respectively, for pumping fluid through the pipes 20 and 22. Thepumps may be, for example, positive displacement pumps, such as, e.g.,reciprocating pumps, rotary pumps, or diaphragm pumps, and may belocated anywhere in the system (e.g., in-line within the pipe or in areservoir tank) where they can effect movement of fluid through thepipes with sufficient force to achieve separation of muscle tissue fromconnective tissue and to break muscle tissue down to the desiredparticle size. Conventional lobe-type and progressive cavity food pumps,for example, as manufactured by Roots, G&H, and Mono (Mono Pumps Ltd,Manchester, U.K.), can be employed. Alternatively, any fluid pumpcapable of generating sufficient outflow of fluid can be employed,including, for example, centrifugal pumps (e.g., radial flow, axial flowand mixed flow pumps), jet pumps, peristaltic pumps, or vane pumps.Alternatively, any pump or other device capable of imposing stress(tensile, shear or normal) so as to preferentially cause mechanicalfailure in the muscle tissue, as opposed to the connective tissue, canbe used. One particularly useful pump is a low shear pump, e.g., apiston pump. Pressure differential can range from negligible to thelimit of the pump, although near the pressure limit, excess shear can beintroduced to the detriment of process efficiency. In some embodiments,a bell suction for the pump may be provided to prevent pump cavitationand resultant shear.

In certain embodiments, the reservoir tanks can be replaced with coilsof pipe which can hold the slurry in a relatively undisturbed state orserve as a conduit through which the slurry can be pumped. Theconstriction can be contained within the coil of pipe, e.g., where thespace in which the system is to be placed is small.

The pipes 20 and 22 each have a reduction fitting 26 of a diameter lessthan that of the remainder of the pipe such that fluid being pumpedthrough the pipe is subjected to an acceleration. This accelerationresults in the contents in the pipe being subjected totensile and shearforces. The amount of tensile stress is selected to be below the levelwhere a substantial fraction of the connective tissue will fail (e.g.,tear) and above a level where a substantial amount of the muscle tissuewill fail (e.g., tear). The ratio of tensile to shear stress is selectedto be high. In general, the suitable amount of stress is a function ofthe hydration or dwell time of the animal tissue in the aqueous solventand the strength of the muscle tissue of the particular animal. Forexample, beef is generally “tougher” than fish, and will generallyrequire higher amounts of stress, longer hydration period, and/or bothto achieve similar results. Thus, where space is available, tissue canbe processed by leaving it to hydrate for longer periods of time andapplying lower amounts of stress. Conversely, where space is at apremium, e.g., on a factory trawler, hydration times can be kept to aminimum (e.g., about one minute) or avoided, and the applied stress canbe higher to accommodate the higher strength of the muscle tissue thanmight otherwise be achieved through longer hydration times.

Generally, the tensile and shear forces are provided by pumping thecontents of the reservoir tank through a pipe that is configured toresult in a rapid acceleration of the fluid, e.g., a pipe which has aconstriction therewithin. Such an acceleration can be achieved, forexample, by causing the cross-sectional area throne) which the fluid ispumped to decrease, resulting in an increase in the fluid flow speed.FIGS. 4A and 4B illustrate exemplary alternative constrictionconfigurations that will result in such an increase in flow speed,including a valve 252 (FIG. 4A), e.g., a ball valve, and a baffle 254(FIG. 4B). In certain embodiments, elbows in the pipe, e.g., one or more90 or 45 degree fittings, or one or more helices or coils in the pipemay also function as a constriction, as they can apply sufficient stressto fluids passing therethrough. Embodiments may include one or more ofany of these configurations. In some embodiments, the acceleration thatresults from the pumping of fluid from the reservoir tank into the pipeis sufficient to effect the separation of muscle from connective tissue,and no additional configurations required.

One particularly useful combination is a positive displacement pump anda ball valve constriction. One advantage of such combination is that itallows for the concentration of the total stress in the form of tensilestress (rather than from shear stress), which typically preferentiallycauses failure in the muscle. Another advantage is that it allows theoperator direct and separate control of the energy delivered per unittime and of the flow rate. For example, partially closing the ball valveagainst flow generated by a perfectly positive displacement pump affects(increases) only the energy delivered. Closing a ball valve against acentrifugal pump, on the other hand, will decrease flow and may, in someranges of closure, increase the total energy delivered per unit time(due to changes in flow and viscosity). In some closure ranges, suchclosure against a centrifugal pump can decrease power consumption, andconsequently reduce the rate at which work is delivered.

Further referring to FIG. 3, a terminal pipe 24 leads from the reservoirtank 16 to a refiner 40, which is described in more detail below. Asshown in this embodiment, pipe 24 has a pump 34 for pumping fluidthrough the pipe 24, and has a reduction fitting 26, although theterminal pipe may optionally lack one or both of these features. Acollection channel 50 extends below refiner 40 for collecting proteinpaste that passes through a screen 42 on the refiner 40, while anoutflow tray 56 collects material that does not pass through the screen42 and is expelled from the terminal end 44 of the refiner.

Separation Devices

A separation device is illustrated in FIG. 5, in which the separationdevice is a refiner 40 that includes a cylindrical screen 42 having aintroduction end 43 and a terminal end 44. A series of paddles 46 extendfrom a central axis shaft 48 radially toward the screen 42 and areconfigured to rotate within the cylindrical screen 42. The paddlesextend in a generally longitudinal direction along the interior of thecylindrical screen 42. The refiner is configured such that, as theanimal tissue slurry is introduced into the introduction end 43, theprotein paste can pass through the mesh of the screen 42, while thelarger connective tissue fragments cannot so pass. The paddles 46 have apitch such that, as the paddles rotate within the cylindrical screen 42,they move the material that does not pass through the screen from theintroduction end 43 to the terminal end 44 of the cylindrical screen,where it is expelled onto the outflow tray 56. The refiner can have one,two, three, four or more paddles. Generally, the greater the number ofpaddles, the lower the RPM's required to handle a given capacity ofslurry, as described below.

The rotation of the paddles in certain embodiments forces or assists inthe proteins and/or muscle particles' passing through the screen 42. Theamount of force generated by the paddles is determined by the rotationalspeed of the paddles, the relative stiffness of the paddle material, andthe proximity of the paddles to the screen. The paddles in certainembodiments rotate at speed no more than about 1000 RPM (e.g., no morethan about 700 RPM, 500 RPM, 450 RPM, 400 RPM, 350 RPM, 300 RPM, 250RPM, 200 RPM, 150 RPM, 125 RPM, 100 RPM 90 RPM, 80 RPM, 70 RPM, or 60RPM). In some embodiments there is no natural upper limit on paddlerotation speed, e.g., paddle rotation speed can be greater than about1000 RPM. The gap between the paddle and the screen may be no largerthan about 50 mm (e.g., no larger than about 40 mm, 30 mm, 20 mm, 10 mm,5 mm, 2.5 mm, 1 mm, 0.5 mm, or too small for conventional measurements).In certain embodiments, gaps larger than about 50 mm may be employed(e.g., larger than about 60 mm, 70 mm, or 80 mm). In other embodiments,there is no substantial distance between the screen and the paddle,i.e., the paddle contacts the screen. In some embodiments, the refinerwill permit the setting of the distance between the paddles and thescreen. In certain embodiments, the refiner is a straight-type refiner.In certain embodiments, the refiner is a taper-type refiner. Suitablerefiners include, for example, those manufactured by BrownInternational, of Covina, Calif. (e.g., the Brown model 202,402), or FKCLtd., of Fort Angeles Wash. (e.g., the FKC models 350 and 450). Thesemachines are also sometimes referred to as pulpers, polishers, and/orfinishers. Any size can be used depending upon the desired capacity.Generally, the smaller the degree to which the muscle tissue is reducedin particle size, the smaller the refiner that is required for a givencapacity, and conversely, the larger the particle size of the muscletissue, the larger the refiner that is needed to achieve the givencapacity.

The size of the gaps in the screen mesh determines, at least in part,the particle size of the material that can pass through the screen.Generally, the gaps in the screen mesh are selected such that themajority of the protein component will pass through the screen, whilethe majority of the connective tissue remains within the cylindricalscreen where it is expelled by the action of the paddles. In certainembodiments, the screen is formed of a mesh having holes no larger thanabout 2 mm (e.g., no larger than about 1.75 mm, no larger than about 1.5mm, no larger than about 1.25 mm, no larger than about 1 mm, no largerthan about 0.75 mm, no larger than about 0.5 mm, and no larger thanabout 0.25 mm, no larger than about 0.05 mm) In certain embodiments,holes larger than about 2 mm may be employed (e.g., holes larger thanabout 2.5 mm, holes larger than about 2.75 mm, holes larger than about 3mm, holes larger than about 3.5 mm, holes larger than about 4 mm) Forexample, when processing fish, the holes in the screen mesh typicallyrange from about 0.25 mm to about 1.5 mm.

In certain embodiments, the refiner can include a cylindrical screen,which itself rotates, for example, to produce a centrifugal force thataids in moving the proteins through the screen. The paddles in such arefiner can be held relatively motionless, e.g., not be rotated, or canthemselves rotate, typically in a direction opposite the screen.

In alternate embodiments, the separation device can include a flat orcurved screen and one or more paddles that sweep across the surface ofthe screen, sweeping off connective tissue and, optionally, assisting inforcing protein, e.g., muscle protein, through the screen. In stillother embodiments, the separation device can include a flat or curvedscreen, for example, a flat or curved screen set at an angle fromhorizontal, that is moved from side to side, e.g., vibrated or shaken,which allows gravity to cause the protein particles to pass down throughthe mesh. Optionally, the movement of the screen combines with the angleof the screen to move material that collects on the screen to an edge ofthe screen and optionally off the edge.

In another embodiment, the separation device can be a belt-typeseparator, such as a Baader™ 607, with a drum equipped with small holes(the current minimum standard is 1.3 mm, however, smaller holes aretechnically possible and available on a custom-made basis). Theseparation device can be equipped with an injection device having anozzle that has been machined to fit on the outside of the drum, e.g.,the nozzle contacts an element made of ultra high molecular weightplastic that contacts the drum. The element has a curved side thatcomplements the curve of the drum. The nozzle connects the separationdevice to the reservoir tank and/or pipes configured to rapidlyaccelerate the slurry. This nozzle delivers the slurry through arectangular orifice, or a series of small perforations across an areawhose width is less than the length of the drum. The Baader™ 607equipped with a Baader™ part number 9100001228 is an example of such anassembly for delivery of the slurry to the center of the drum. Deliveryof the slurry into the center of the drum (generating even distribution)is preferred to delivery to the edges of the drum.

The reservoir tanks, pipes, pumps and separation devices are all formedof materials suitable for handling food, including, for example,stainless steel (e.g., type 304 stainless steel, type 316 stainlesssteel), carbon steel, aluminum, glass, and/or plastics.

Recirculating Tank System

In certain embodiments, multiple hydration and acceleration steps arecarried out in the same reservoir tank, pipe, and pump. FIG. 6Aillustrates such a recirculating reservoir 101, which includes areservoir tank 100 and a recirculating pipe 102 that is connected at aninlet 104 and an outlet 106 to the tank 100. A restriction fitting 108is located in the recirculating pipe 102 and has an inner diameter lessthan that of the remainder of the pipe 102. A pump 110 is located in therecirculating pipe 102 and is configured to pump fluid from the tank 100through the recirculating pipe, including the restriction fitting 108,and back into the recirculating reservoir tank 100. A discharge pipe 120leads from the reservoir tank 100 to the refiner, not illustrated. Adischarge pump 122 is operative to pump fluid from the reservoir tank100 through the discharge pipe 120. This embodiment allows for therepeated hydration and acceleration of animal tissue without the needfor additional tanks, pipes and pumps, which permits a reduction in thecapital investment required to set up such a system and reduces thefloor space required to effect the separation of protein.

Alternatively, as illustrated in FIG. 6B, the slurry can be acceleratedwithin tank 100, e.g., by a submersible pump 110 that continuouslyforces a portion of the slurry through a constriction 108 in pipe 102,or, e.g., by paddles that accelerate the slurry. For example, pump 110can be located at the bottom of the tank, and can circulate slurry thatenters pump 110 through inlet 112 and exits the pump through outlet 114into pipe 102 contained within tank 100 and having a constriction 108therein. The pipe can discharge the slurry directly back into the tank.The pipe can, for example, be in the middle of the tank or along a sideof the tank. In this embodiment, the slurry does not leave the tank(avoiding, e.g., leaks), and a separate pipe directs the finishedproduct to the separation device.

In such a continuous system, the average period of time that a particleremains in the tank, e.g., in a hydration period, is a function of thetank volume and the pump flow.

Separated Protein Slurry

Further referring to FIG. 1, the separated protein slurry 324 thatresults from this process in certain embodiments contains water, solubleproteins and insoluble proteins. A substantial amount of the insolubleproteins are in myofibrillar filament form. (e.g., more than about 50%,60%, 70%, 75%, 80%, 90%, or 95% of the insoluble proteins in the slurryare in myofibrillar filament form). For example, substantially all ofthe myosin in the product can be in myofibrillar filament form (e.g., atleast 75%, 80%, 90%, or 95% of the myosin). The separated protein slurrymay, in certain embodiments, contain a relatively small amount ofconnective tissue. For example, in certain embodiments, the proteinslurry may contain less than about 10% by weight, relative to the amountof protein in the slurry, connective tissue (e.g., less than 10%, 5%,4%, 3%, 2%, or 1% by weight, relative to the amount of protein in theslurry, connective tissue).

The amount of undissolved protein, e.g., insoluble protein, can bemeasured using methods known in the art. For example, by firstseparating, e.g., by filtering or pelleting (e.g., by centrifugation)undissolved protein from the separated protein slurry, followed byquantifying, e.g., by weighing, of the undissolved protein. Once theundissolved protein has been separated, the amount of myofibrillarprotein present can be measured. Sarcoplasmic protein can be extractedfrom the undissolved protein pellet by standard techniques. Myofibrillarprotein can be extracted from the remaining fraction by standardtechniques (e.g., resuspension in a phosphate buffer, homogenization,and centrifugation) and quantified, e.g., by weighing. The amount of thedissolved protein remaining in the separated protein slurry afterremoving the undissolved protein, can be measured, e.g., after removing,e.g., by evaporating, the aqueous liquid. The quantification can becarried out by, e.g., weighing the protein.

Sources of Animal Tissue

The animal tissue from which the separated protein slurry is derived canbe obtained from any animal food source, e.g., fish, shellfish (e.g.,shrimp, crab, lobster, krill, clams, muscles, scallops, and crayfish),squid, poultry, beef, lamb, or pork. In certain embodiments, the sourceof animal tissue is the parts of the animal that remain after otherparts of the animal have been removed for retail sale, for example, theparts of the fish that remain after the fish has been filleted, or theskeletons of chickens after the chickens have been butchered. In someinstances, such material is not used for human food. In someembodiments, the animal tissue may have already undergone someprocessing, and may contain a large amount of connective tissue, e.g.,more than 70%, e.g., more than 80%, e.g., more than 90% of connectivetissue by weight.

In certain embodiments, the animal tissue source is subjected topreliminary treatment steps appropriate for the animal type. Forexample, where fish are to be processed, the fish are generally guttedand the head removed. An external belt/drum deboner or mincer (e.g., asmanufactured by Baader™, Toyo, or Bibun), e.g., having hole sizes ofbetween about 1.3 mm and about 8 mm, may be employed, for example, wherea large portion of the connective tissue is comprised of sheets such asskin and muscle sheaths, as occurs, e.g., in white fish. Optionally, thefish is filleted, with either the fillet or the remaining fish portionsbeing utilized as the animal tissue.

Where the food source is poultry, beef, lamb, or pork, the animal isgenerally butchered, the skin is optionally removed, and the carcass iscut into sections. The sections are optionally deboned (e.g.,mechanically deboned or manually deboned and, optionally, includinggrinding and/or crushing the bones and separating, e.g., by filtering,bone from the remainder of the animal tissue) and the cartilage isremoved. In certain embodiments, the sections are deboned by blastingthe sections with high-pressure water to separate the muscle andconnective tissue from the bone and cartilage. For example, the sectioncan be placed on a screen and moved past an array of nozzles sprayinghigh-pressure water (e.g., at least 250 PSI, at least 275 PSI, at least300 PSI, at least 325 PSI, at least 350 PSI, at least 375 PSI, at feast400 PSI). The screen has a mesh sized to permit the particles of softtissue (e.g., muscle and connective tissue) to pass through, while beinglarge enough to retain substantially all of the bones. Such treatmentmay prevent the release of blood and other unwanted material from thebones and cartilage that would occur during crushing that is carried outduring many current separation techniques. The resultant tissue can thenbe added to the reservoir tank for hydration, optionally with grindingor mincing (e.g., using a grinder, Beehive or Paoli separator, or silentcutter such as a Stephan silent cutter) occurring prior to adding thetissue to the reservoir tank.

Pre-Separation Processing

Optionally, fat content in animal tissue can be reduced prior tohydration and/or further processing. It is possible to reduce fat of thetissue in the reservoir tank prior to processing due to the lowerdensity of fat relative to protein and due to low emulsificationcapacity of protein at and around the isoelectric point of the protein(approximately 5.5). Fat can be reduced, e.g., by chilling thesuspension, e.g., to close to freezing temperature, e.g., to about −1°C. or lower, e.g., to about −28° C., reducing the pH of the suspension,e.g., to close to the isoelectric point of the protein, e.g., to pH ofabout 5.5, and/or bubbling air through small perforations in a pipe orgrid into the suspension (see, e.g., Example 5), and removing the fat.Fat removal can be performed in a continuous and/or batch process.

Post-Separation Processing

Once protein, e.g., muscle protein, e.g., myofibrillar and/orsarcoplasmic protein, has been separated from connective tissue, theprotein can be farther processed as desired. During separationprocessing described herein, substantially all muscle protein can remainundissolved, e.g., at least 50% of muscle protein can remainundissolved. The amount of undissolved protein can be measured, e.g., byfiltering or pelleting (e.g., by centrifugation) undissolved proteinfrom the separated protein slurry. The amount of dissolved proteinremaining in the separated protein slurry after removing the undissolvedprotein, can be measured, e.g., after removing, e.g., evaporating,aqueous liquid. After separation, the undissolved protein, e.g., muscleprotein, can, for example, be solubilized by mixing it with water andraising the pH to dissolve the protein as described in U.S. Pat. No.6,136,959, or can be solubilized at a pH below about 3.5, as describedin U.S. Pat. Nos. 6,005,073, 6,288,216 and 6,451,975. These patents arehereby incorporated by reference in their entireties. In either case, asthe connective tissue has already been separated from the muscleproteins, there may be no need for filtering, pumping, or centrifugingthe proteins. The dissolution and coagulation of the proteins can becarried out in a single tank, eliminating the need to transfer theproteins. The separated protein slurry need not be subject to afiltering step, although in certain embodiments, additional filtrationmay be desired. The result is the enablement of more gentle treatmentand easier handling of the protein, and the reduction of or eliminationof the creation of foam. The protein can also be used to make a pastemade of fish protein.

In certain embodiments, the separated protein slurry is dewatered.Dewatering can be accomplished by running the material through one ormore screens followed by decanting or squeezing out the water using ascrew press. Dewatering may also be accomplished by centrifugalseparation of the water, spray drying, evaporating, or freeze drying.

In certain embodiments, muscle tissue is separated from connectivetissue, and the particle size of the muscle tissue is reduced to a sizesufficiently small that it can be injected directly into intact musclefoods (e.g., meat), for example, to enhance the water-holding capacity,texture, and/or taste of the muscle food. In certain embodiments, themuscle particles are mixed with minced muscle to control water holdingcapacity and/or texture of the minced muscle, e.g., gelation.

In certain embodiments, where the animal tissue being processed containseither no extraneous material that is per-se objectionable (e.g., boneor cartilage) or contains an acceptable amount of such (e.g., a lowlevel of connective tissue), the tissue can be ground to an appropriatesize (e.g., a size whereby the connective tissue is sufficiently smallto avoid any problems, e.g., where the connective tissue fragments aresufficiently small to be injectable and/or not detrimentally affect thetaste and/or texture of the final meat product) and run through thehydration/acceleration process to further reduce the particle size ofthe tissue. The resulting fluid, which includes soluble proteins,insoluble proteins, and optionally some connective tissue, can then becombined with muscle foods (e.g., intact muscle), for example, byinjection into the muscle food or by tumbling with the muscle food,optionally, under vacuum. In some embodiments, the fluid is added tomuscle foods as is, without inclusion of any further additives. Thefluid can optionally include additives, e.g., salts, buffers, acids,and/or bases, added to aid in the distribution and/or solubilization ofthe proteins. The majority of the insoluble proteins can be inmyofibrillar filament form (e.g., more than about 50%, 60%, 70%, 75%,80%, 90%, or 95% of the proteins in the slurry are in myofibrillarfilament form). For example, substantially all of the myosin in theproduct can be in myofibrillar filament form (e.g., at least 75%, 80%,90%, or 95% of the myosin). This process can be used, for example, toincrease the protein content of muscle foods. Without being bound to anyparticular theory, this method of increasing protein content of musclefoods, takes advantage of reduced viscosity of muscle protein in theadded fluid. This process can also be utilized for other purposes, e.g.,to increase the water content of muscle foods and/or to replace waterlost by muscle foods upon freezing and thawing. For example, fish canlose between about 10% and 20% of its water content in the freezingprocess, and the fish tissue may at that point not be able to retainpure water injected into the tissue. The presence of the protein canresult in retention of water by muscle foods.

EXAMPLES

The invention is further described in the following examples, which donot limit the scope of the invention described in the claims.

Example 1

Gutted and headed fish were ground to a size of about ¼ inch and thenmixed with water in a ratio of 1 part water to 1 part fish and placed ina reservoir tank. The fish tissue was allowed to sit in the water for 5minutes, during which time the muscle tissue at least partiallyhydrated. The resulting slurry was pumped using a positive displacementpump through 3-inch ID pipe at a rate of 5 ft/sec. The pipe had a 3-inchlong restriction fitting having an inner diameter of 1 inch. As theslurry was pumped through the pipe and reduction fitting, the slurryaccelerated, applying force to the particles of fish tissue within theslurry and tearing the hydration-weakened muscle tissue from theconnective tissue. Muscle tissue was also torn apart, reducing theparticle size of the muscle particles. The pipe directed the slurry intoa second reservoir tank, where the slurry incubated for an additional 5minutes, allowing for additional hydration of the muscle tissue. Theslurry was then pumped through the restriction fitting and into anotherreservoir tank. This process was repeated through ten cycles to achievethe desired particle size and/or particle size distribution.

The slurry was then introduced into a refiner having screen holes of0.25 mm. The paddles of the refiner were set to run at 60 RPM. Theproteins and water passed readily through the screen, while theconnective tissue, which had not been reduced in size to the sameextent, did not pass through the screen. The protein and water werecollected to yield a separated protein slurry having the consistency ofwhite glue.

Example 2

A beef brisket was cut into 1-inch pieces and ground through a ¼-inchplate meat grinder. The resulting ground meat was then placed in waterin a ratio of 1 part meat to 2 parts water to form a slurry. The slurrywas agitated in a Cuisinart® food processor with a 3-inch diameterimpeller having rounded edges (to reduce shear) at about 1750 RPM forfive one-minute intervals, with two minutes hydration time betweenagitations. The slurry was then separated with a 1.5 mm swept screen,aided with an internal water spray. Connective tissue was caught on thescreen, while separated muscle proteins that were suspended in the waterpassed through the screen holes.

Example 3

Chinese white shrimp, deheaded and with the shell on, were chopped alongwith an equal amount of ice in a Stephan chopper for three minutes. Thechopped shrimp were then agitated with an additional five parts waterwith a mixing hook (which includes several loops arranged into a whisk)having a 3-inch diameter, for 30 minutes at 120 RPM. The resultingslurry was then separated in a swept 1.5 mm screen aided with aninternal water spray. Shells and connective tissue were caught in thescreen, while suspended muscle tissue passed through the screen holes.

Example 4

Fillets of pollock were chilled to 32° F. and cubed into ½-inch pieces.Samples were then mixed with water (in ratios described below) andchopped in a Stephan cutter, model PCM12, with a two-bladed curved knifeattachment at high speed for four minutes to reduce the particle size ofthe pollock fillets to a point at which the resulting slurry had apaste-like consistency.

A first batch of cubed pollock was mixed with ½ part water and formedinto the slurry as described. The shiny was tumbled with 8 parts pollockfillets in a vacuum tumbler, at which point the fillets absorbed orotherwise retained the bulk of the slurry. After tumbling, the mixturewas put into a standard 16.5 fish block frame, an aluminum c-shapedframe used in forming fish sticks, with, a Beck liner®, a cardboardliner designed to allow water to enter the liner. This was frozen in aplate freezer at a pressure of about 10 PSI to 0° F. The resultant fishblock had a higher amount of protein than it would have had absent thecombination with the slurry, producing an enhanced recovery fish block,and retained its form upon thawing.

A second batch was used to rehydrate previously frozen fish, which lostsome water upon freezing. The batch was mixed with 3 parts water,reduced to a paste, and injected into previously frozen (andsubsequently thawed) fillets of Pacific cod to a total marinadeinclusion of 10% by weight, thus replacing some of the moisture lost inthe freeze/thaw process and increasing the protein content of thefillets.

A third batch was treated in the alkaline process described in U.S. Pat.No. 6,136,959, and the resultant isolate was adjusted to a proteincontent of 5% and injected into Pacific cod fillets at an inclusion of15% by weight through an injection needle with an ID of 1 mm, thusincreasing the water and protein content of the fillets.

Example 5

One hundred pounds of Tilapia fillet trimmings, which included largepieces of non-muscle protein and significant quantities of fat, werereduced in size in a Baader 695 belt-mincer to 5 mm pieces. These weremixed with water (including ice) at a solids content of 3% and the pHwas reduced to 5.5 using HCl. This mixture was agitated gently in acircular tank. Air was injected into the tank through a pipe with 4,¼-inch perforations at 15 PSI. Large quantities of fat were thusseparated. This fat rose to the surface and then migrated to the centerof the tank and was easily removed by skimming.

The pH was then raised to 8.0 and pumped directly at 50 gpm through aball valve with a pressure drop of 100 psi into a Brown 204 refiner with0.5 mm holes.

This product was treated in the alkaline process described in U.S. Pat.No. 6,136,959, and the resultant isolate was adjusted to a proteincontent of 3.5% and injected into Pacific halibut fillets at aninclusion of 20% by weight using a Fumako injector. These fillets showedreduced cook loss compared to a phosphate based marinade, and thecharacteristic flavor of tilapia fat could not be detected.

Example 6

Chicken breast meat was ground through a ¼-inch plate in a conventionalmeat grinder producing 300 pounds of ground chicken meat. The meat wasmixed with water to a solids content of 3%. The pH was adjusted to 5.3with HCl. The fat separated more easily than expected and coagulatedinto yellow globules, which were easily skimmed from the reservoir tank.The slurry was agitated across a ball valve restriction for 30 minutes.The valve was adjusted so as to increase the amperage of the pump drivemotor by 1.2 amps @ 480 volts.

Because of the large diameter of the connective tissue, and the tendencyof the tendons to braid themselves into “ropes” of even larger diameter,the paddles in the Brown refiner used in this process were set at arelatively large 15 mm gap with the screen. To compensate for the largegap, refiner RPM was increased to 700 RPM. This setup proved superior inreducing the amount of connective tissue in the product relative to thesmall gap-low RPM methods used in fish.

Other Embodiments

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention. Forexample, while a refiner is disclosed above as a means for separatingthe protein from the connective tissue, a screen, conventional refiner,strainer, or other device for sorting large particles from smallerparticles, or strong particles from weaker particles, can be employed.

As another example, while pumps have been described for moving fluidthrough pipes, fluid could instead be moved through the pipes throughthe effects of gravity or pressure, e.g., by pressurizing a column ofair above the surface of the fluid.

Accordingly, other embodiments are within the scope of the followingclaims.

What is claimed is:
 1. A method of separating muscle protein fromconnective tissue, the method comprising: (a) reducing the size of themuscle tissue which contains both muscle protein and connective tissue;(b) mixing the muscle tissue with an amount of water to create a firstslurry; (c) pumping the first slurry through a first pipe and thenthrough at least one constriction, thus causing the first slurry toaccelerate in the direction of the flow of the first slurry such that asubstantial fraction of the connective tissue will not tear and asubstantial fraction of the muscle protein will tear; (d) separating themuscle protein from the connective tissue using a separation device; and(e) solubilizing the separated muscle protein in a second slurry byraising or lowering the pH of the second slurry to a point at which atleast 75% of the separated muscle protein dissolves; wherein thecompletion of steps (a)-(e) results in a separated muscle protein of asufficiently small size that it can be injected directly into intactmuscle foods; and (f) dewatering the solubilized, separated muscleprotein by centrifugal separation of the second slurry.
 2. The method ofclaim 1, wherein step (e) comprises raising the pH of the second slurryto at least about 10.5.
 3. The method of claim 2, further comprising,prior to step (f), precipitating the solubilized, separated muscleprotein by lowering the pH of the second slurry to about 5.5.